Swift: How to get substring from start to last index of character

Question

I want to learn the best/simplest way to turn a string into another string but with only a subset, starting at the beginning and going to the last index of a character.

Answer 1

edit/update:

In Swift 4 or later (Xcode 10.0+) you can use the new BidirectionalCollection method lastIndex(of:)

func lastIndex(of element: Element) -> Int?

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let string = "www.stackoverflow.com"
if let lastIndex = string.lastIndex(of: ".") {
    let subString = string[..